When I first thought of this episode it sounded like a great idea, because the way TV and movies abuse our understanding of medicine and the human body has always bugged the hell out of me. But now that I've put in the research and checked out all the facts, I realize that I'm merely being a huge party pooper. If you've enjoyed believing in some of these fancies, you're probably going to be mad at me. Or better yet, just proclaim that I'm on the payroll of corporate interests, ignore everything I have to say, and go on believing that eating chocolate causes acne.

And that's as good a starting place as any. Folk wisdom tells us that eating chocolate causes acne, or that the oil from cheap greasy food like cheeseburgers or french fries will ooze right out through your skin and cause pimples. Fortunately, numerous trials have been done, and we've learned that groups eating the suspect foods don't get any worse acne than the control groups eating healthy food. So you can keep right on chowing down. The true causes of acne are heredity, hormonal changes associated with adolesence, stress, and bacteria, though some recent studies have found minor correlations with consumption of foods high in iodine. So don't drink iodine if you're pimply.

If you enjoy the taste of chocolate, you've probably also heard that taste buds are arranged on the tongue in different regions, and each region is sensitive to a particular taste. Bitterness is sensed on the tip of the tongue, sweetness on the edges, and so forth. Turns out this is another myth too. Every taste bud senses all flavors. This explains why it never works when you try to test that old story by squeezing lemon onto just little dots of your tongue, and find that it's pretty horrible no matter where you put it.

So long as we're talking about food and the senses, let's mention the old tip of improving your vision by eating carrots. As it turns out, the only connection between carrots and eyesight is the vitamin A that your body derives from the beta-carotene in carrots. You can eat all the vitamin A you want and it won't improve or otherwise affect your vision at all. If you have a severe vitamin A deficiency, it can lead to one cause of blindness. It's not quite clear how this story got started, but one source says it was a misinformation campaign by the Royal Air Force in World War II to explain the effectiveness of their night fighter pilots — the actual classified explanation being their new radar system.

Another food that's said to help is orange juice and cookies to replenish your blood sugar after you give blood. The problem with this is that there's no reason your blood sugar would be any lower or require replenishment after donating. Giving blood just sucks a safe amount of your blood reserve out of your body; it does not change or weaken the blood that remains. Nor is the rest of your body dehydrated after giving blood, so there's no more reason that you would need to rehydrate than there might otherwise be. Some people might get nervous or faint from the process, and the refreshment might help to relax them; but there is no medical need for juice, cookies, flowers, kind thoughts, or anything else.

While we're on the subject of blood, let's talk about one of my pet peeves from Hollywood. In Pulp Fiction, John Travolta stabbed Uma Thurman with a syringe full of epinephrine directly into her heart to cure a drug overdose. In The Rock, Nicolas Cage does the same thing to himself to counter the effects of poison gas. Wow, makes for a dramatic movie scene, doesn't it? And now, since it was such an exciting scene, practically every TV and movie writer thinks it's real and puts it into about every other show. Well I'm sorry to burst your epicardium, but according to emergency room doctors, there is no actual medical treatment that involves the dramatic stabbing of a huge needle directly into the heart — certainly not through the breastbone or in any kind of violent or forceful manner. The way to get any medication into the heart is to simply inject it into a vein. No driving musical soundtrack required.

Of course, if you did accidentally kill your friend by stabbing them in the heart with a syringe, you might get to test the old story that their hair and fingernails will continue growing after death. There's no truth to this either. Metabolism stops at death, so there is no possible mechanism by which new hair or fingernails could be created. This rumor probably got started because a dead body's soft tissues dry out and shrink and pull away, exposing more of the hair and nails. Egyptians didn't really look that creeped out in real life.

Neither does hair grow any thicker or darker after it's been cut. Everyone's been told this, but nobody seems to believe it. Hair is made of dead cells. There is no metabolism or living nerves in hair, thus no mechanism by which the tip of a hair follicle could communicate that it had been cut back to the root to stimulate additional growth or the development of new hair follicles. Some people have longer hair and some people have shorter hair, both on their head and on their bodies, and the speed of growth and the lifecycle of the follicles is determined by your genes. It can't be changed, certainly not by anything as simple as cutting. A cut-off tip of hair is more visible than the finely tapered natural end, which probably explains why so many people still believe this; but that cut hair will never be as long as the natural hair.

Here's a good one, and it's a personal favorite because it happened to a friend of mine. He staggered up out of the water in Cancún with a Portuguese Man-o'-War stuck to his shoulder, tentacles glued all over his torso, and collapsed on the beach writhing in agony. While someone called for help, some gringo SCUBA divers on hand offered to help the way they knew best: All six of them unzipped and hosed him down liberally. Sadly for my friend, the old home remedy of urinating on a jellyfish sting only makes things worse. While vinegar will in fact block any remaining stinger cells from firing, urine contains ammonia, which causes the stinger cells to fire. Let's just say it was a bad day for my friend.

On a less painful subject, who among us does not have a mom who has whacked us with a ruler for cracking our knuckles? Folk wisdom says knuckle cracking leads to arthritis or joint enlargement. As a lifelong knuckle cracker, I can confidently attest to no ill effects. Nor should I expect any. The crack you hear is simply the popping of bubbles within the synovial fluid as the ligament is stretched, as hard to believe as that sounds. It causes no problems and has no cumulative effects. While the popping itself is harmless, the repeated stretching of the ligaments can lead to, well, stretched ligaments, but this too is unrelated to either arthritis or enlargement. Never pay attention to your mother. I'm pretty sure my own mom's not listening, so I can say that.

Have we had enough of these yet? How about one more?

Remember in Beverly Hills Cop, when Judge Reinhold said to Sgt. Taggart that the average person has five pounds of undigested red meat in their bowels? Urban myths like this one are largely responsible for the popularity of colon cleansing in holistic medicine. The hose enters through the exit and some solution is pumped in to rinse out the daily output of your digestive system. This is based on a wholly erroneous assumption, that you have old junk or "toxins" built up in there. You don't. The digestive system is an active, working, one-way conveyor belt. Nothing stops and stays in there. If it does, that's called a blockage, which is a serious medical emergency. Unless you are in the emergency room right now with an intestinal blockage, there is nothing in your intestines older than about 24 hours, other than bacteria which live safely tucked away in the walls. If you've ever had a colonoscopy, you know that all you have to do is stop eating and drink water for a day or two and your bowels will be as clear as a Smurf's conscience.

Whenever you hear a story or a rumor about the human body that seems unusual or doesn't make any obvious sense, be skeptical. It may be true after all — the body is a fascinating machine that's full of surprises — but it's always best for your health to follow a skeptical process and determine the facts for certain.